Methods have been developed for the proliferation in vitro of human and rat retinal pigment epithelium (PE). Research is proposed to gain more understanding of the properties of the PE by studying the PE in vitro. The effects of varying intracellular cyclic AMP concentrations on phagocytosis of isolated rod outer segments will be studied, and the possible influence of light, calcium, hormones, and other agents on phagocytosis and intracellular cyclic AMP will be investigated. Liposomes of different phospholipid composition will be used as a model of the outer segment membrane to study how lipid composition and surface charge influence phagocytosis of these liposomes by normal rat PE and by PE of Royal College of Surgeons (RCS) rats with a known hereditary defect in the phagocytosis of rod outer segments. The relationship between glycoconjugate (proteoglycan and glycoprotein) synthesis, vitamin A metabolism, and phagocytosis will be studied in normal and RCS rat PE. Specialized biochemical properties fo PE (vitamin A ester synthesis, cellular retinol binding protein content, and tyrosinase activity) will be compared in primary cultures and subcultured cell strains of human PE in order to assess whether these properties are retained by PE cells after extensive proliferation in vitro. These studies will provide a basis for comparing subcultured PE cell strains from normal postmortem donors and from postmortem donors with retinitis pigmentosa which are currently maintained in this Laboratory.